Oxygen-scavenging containers having low haze

ABSTRACT

A container providing effective oxygen-scavenging functionality, while having low haze. The container has at least one wall, wherein the wall comprises a populated area, and wherein the populated area comprises a film-forming polymer; and a population of particles comprising an effective amount of oxygen-scavenging particles, wherein the number of particles of said population does not exceed a concentration of about  
     (6×10 7  particles÷T) per cubic centimeter of polymer  
     wherein T is the thickness of the populated area in mils; and wherein the wall has a transmission Hunter haze of up to about 1 percent per mil of the container wall.

CROSS-REFERENCE

[0001] This application is a continuation-in-part of pending applicationSer. No. 09/916,671, filed on Jul. 26, 2001.

BACKGROUND OF THE INVENTION

[0002] Thermoplastic resins such as polyethylene terephthalate (PET) arecommonly used to manufacture packaging materials. PET processed underthe right conditions produces high strength articles with excellent gasbarrier properties. Foods, beverages, and medicines can deteriorate orspoil if exposed to oxygen. To improve shelf life and flavor retentionof products such as foods, beverages, and medicines, therefore, thebarrier protection provided by PET is often supplemented with additionallayers of packaging material or with the addition of oxygen scavengers.

[0003] Adding a layer of gas barrier film is known as passive-barrierpackaging. Ethylvinyl alcohol (EVOH), Polyvinylidene dichloride (PVDC),and Nylon MXD6, are examples of films commonly used for this purpose dueto their excellent oxygen barrier properties. Using distinct layers ofdiffering materials is not preferred, however, because it adds cost topackaging construction and does not reduce the levels of oxygen alreadypresent in the package.

[0004] Adding oxygen scavengers to the PET resin is known asactive-barrier packaging. This approach to protecting oxygen-sensitiveproducts is two-fold; the packaging prevents oxygen from reaching theproduct from the outside, and also absorbs some of the oxygen present inthe container and from within the polymer matrix. In some applications,small packets or sachets containing oxygen scavengers are added to thepackaging container and lie next to the food. Sachets are generallylimited to solid foods, where the sachet can be readily removed from thefoodstuff and not accidentally ingested. Construction of the sachets andthe cumbersome nature of their introduction into the package result inincreased costs.

[0005] One way to overcome the disadvantages of sachets is toincorporate the scavenger directly into the wall of the food package.This can be done by placing the scavenger throughout the scavenger wallor placing the scavenger in a unique layer between many layers of thecontainer sidewall. It should be appreciated that references to thesidewall and wall include the lid and bottom sides of the container. Atpresent the incorporation of the scavenger throughout the container wallis found in non-transparent trays or packaging films where the scavengeris not visible. Virtually any scavenger can be used in this applicationbecause the scavenger is not visible. However, containers requiringclarity have heretofore been limited to organic type scavengers thatmaintain their clarity when placed in a separate layer in the wall ofthe container. The use of the organic scavenger in a mono-layer orsingle-layer construction is limited by cost and regulatory constraintsdue to the nature of the organic scavenger or the by-products of thescavenging reaction.

[0006] Contributing to the cost is the logistical problems encounteredwith the use of organic type scavengers. In most embodiments, atransition metal catalyst is used to activate an oxidizable polymer. Adisadvantage of this technique is that the polymer begins reacting withoxygen as soon as the package is made. Consequently, the bottles must befilled immediately. Higher amounts of scavenger are used to compensatefor the scavenging capacity lost between the time the bottle is made andwhen the bottle is filled.

[0007] In another technique, UV radiation is used to activate theoxidizable polymer. However, UV activation techniques are relativelyexpensive, and the initiators are often not regulated for use in foodpackaging. Packages designed for beers and juices are specificallydesigned to prevent UV penetration, hence UV activation would not bepractical for these containers which block UV.

[0008] An alternative to a visually acceptable organic material is touse discrete scavenging particles in the container sidewall, such asreduced metal powders. Reduced iron powder is commonly used for oxygenscavenging in food packages. Iron reacts with the oxygen and forms ironoxide. Most applications also utilize a salt and a moisture absorber asreaction-enhancing agents to increase the effectiveness of the ironpowder. Because the reaction usually requires water, the iron scavengingcomposition remains inactive until the package is filled and thereaction is activated by the water of the packaged contents whichmigrates into the polymer and contacts the scavenging composition.

[0009] The use of scavenging powders in clear packages has previouslybeen limited by aesthetics, particularly haze and color. High loadingsof iron powder, on the order of 500-5000 parts per million, aretypically required to obtain sufficient oxygen absorption. Conventionalwisdom and prior art teaches the practitioner to use the highest amountof scavenging surface area possible so that the efficiency and capacityis increased and the amount of iron added is minimized. In practice,this means a large number of small particles. Unfortunately, previousattempts at preparing resin compositions comprising high levels of smallparticles of iron for use in clear packages have resulted in packageswith poor optical properties. This is particularly true when the resincomposition is stretched or oriented to any degree in forming the finalarticle, such as in polyester bottles. Typically, bottles prepared fromsuch resin compositions are translucent. Haze values for these bottlesare generally high, and clarity is lacking.

[0010] Thus, there remains a need for packaging materials havingacceptable visual aspects and comprising activatable oxygen scavengingresin compositions.

BRIEF SUMMARY OF THE INVENTION

[0011] In general the present invention provides a container comprisingan effective amount of oxygen-scavenging particles and having low haze.More specifically, the present invention includes a container having atleast one wall, wherein the wall comprises a populated area, and whereinthe populated area comprises a film-forming polymer; and a population ofparticles comprising an effective amount of oxygen-scavenging particles,wherein the number of particles of said population does not exceed aconcentration of about

(6×10⁷ particles÷T) per cubic centimeter of polymer

[0012] wherein T is the thickness of the populated area in mils; andwherein the wall has a transmission Hunter haze of up to about 1 percentper mil of the container wall.

[0013] The iron or other oxygen scavenger is present in an amountsufficient to effectively scavenge oxygen and provide longer shelf lifefor oxygen-sensitive materials. The particle size of the particlepopulation is optimized to provide effective scavenging activity, whilereducing haze.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is directed to a container and a containerwall. The wall includes a populated area comprising a film-formingpolymer. Suitable thermoplastic polymers for use in the presentinvention include any thermoplastic homopolymer or copolymer. Examplesof thermoplastic polymers include polyamides, such as nylon 6, nylon 66and nylon 612, linear polyesters, such as polyethylene terephthalate,polybutylene terephthalate, polytrimethylene terephthalate, andpolyethylene naphthalate, branched polyesters, polystyrenes,polycarbonate, polyvinyl chloride, polyvinylidene dichloride,polyacrylamide, polyacrylonitrile, polyvinyl acetate, polyacrylic acid,polyvinyl methyl ether, ethylene vinyl acetate copolymer, ethylenemethyl acrylate copolymer, polyethylene, polypropylene,ethylene-propylene copolymers, poly(1-hexene), poly(4-methyl-1-pentene),poly(1-butene), poly(3-methyl-1-butene), poly(3-phenyl-1-propene) andpoly(vinylcyclohexane). Preferably, the thermoplastic polymer used inthe present invention comprises a polyester polymer or copolymer.

[0015] It will be understood that a film-forming polymer is one that iscapable of being made into a film or sheet. The present invention isnot, however, limited to films and sheets. The container of the presentinvention also includes bottle walls, trays, container bases, or lids.The walls of containers such as blown bottles and thermoformed trays canbe considered films or sheets that have been formed into the shape ofthe container, and are therefore also within the scope of the invention.Bases and lids of containers are also considered walls of a container.

[0016] Polymers employed in the present invention can be prepared byconventional polymerization procedures well known in the art. Thepolyester polymers and copolymers may be prepared by melt phasepolymerization involving the reaction of a diol with a dicarboxylicacid, or its corresponding diester. Various copolymers resulting fromuse of multiple diols and diacids may also be used. Polymers containingrepeating units of only one chemical composition are homopolymers.Polymers with two or more chemically different repeat units in the samemacromolecule are termed copolymers. The diversity of the repeat unitsdepends on the number of different types of monomers present in theinitial polymerization reaction. In the case of polyesters, copolymersinclude reacting one or more diols with a diacid or multiple diacids,and are sometimes referred to as terpolymers.

[0017] Suitable dicarboxylic acids include those comprising from about 6to about 40 carbon atoms. Specific dicarboxylic acids include, but arenot limited to, terephthalic acid, isophthalic acid, naphthalene2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediaceticacid, diphenyl-4,4′-dicarboxylic acid, 1,3-phenylenedioxydiacetic acid,1,2-phenylenedioxydiacetic acid, 1,4-phenylenedioxydiacetic acid,succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid,and the like. Specific esters include, but are not limited to, phthalicesters and naphthalic diesters.

[0018] These acids or esters may be reacted with an aliphatic diolhaving from about 2 to about 10 carbon atoms, a cycloaliphatic diolhaving from about 7 to about 14 carbon atoms, an aromatic diol havingfrom about 6 to about 15 carbon atoms, or a glycol ether having from 4to 10 carbon atoms. Suitable diols include, but are not limited to,1,4-butenediol, trimethylene glycol, 1,6-hexanediol,1,4-cyclohexanedimethanol, diethylene glycol, resorcinol, andhydroquinone.

[0019] Polyfunctional comonomers can also be used, typically in amountsof from about 0.1 to about 3 mole percent. Suitable comonomers include,but are not limited to, trimellitic anhydride, trimethylopropane,pyromellitic dianhydride (PMDA), and pentaerythritol. Polyester-formingpolyacids or polyols can also be used.

[0020] One preferred polyester is polyethylene terephthalate (PET)formed from the approximate 1:1 stoichiometric reaction of terephthalicacid, or its ester, with ethylene glycol. Another preferred polyester ispolyethylene naphthalate (PEN) formed from the approximate 1:1 to 1:1.6stoichiometric reaction of naphthalene dicarboxylic acid, or its ester,with ethylene glycol. Yet another preferred polyester is polybutyleneterephthalate (PBT). Copolymers of PET, copolymers of PEN, andcopolymers of PBT are also preferred. Specific co and terpolymers ofinterest are PET with combinations of isophthalic acid or its diester,2,6 naphthalic acid or its diester, and/or cyclohexane dimethanol.

[0021] The esterification or polycondensation reaction of the carboxylicacid or ester with glycol typically takes place in the presence of acatalyst. Suitable catalysts include, but are not limited to, antimonyoxide, antimony triacetate, antimony ethylene glycolate,organomagnesium, tin oxide, titanium alkoxides, dibutyl tin dilaurate,and germanium oxide. These catalysts may be used in combination withzinc, manganese, or magnesium acetates or benzoates. Catalystscomprising antimony are preferred.

[0022] Another preferred polyester is polytrimethylene terephthalate(PTT). It can be prepared by, for example, reacting 1,3-propanediol withat least one aromatic diacid or alkyl ester thereof. Preferred diacidsand alkyl esters include terephthalic acid (TPA) or dimethylterephthalate (DMT). Accordingly, the PTT preferably comprises at leastabout 80 mole percent of either TPA or DMT. Other diols which may becopolymerized in such a polyester include, for example, ethylene glycol,diethylene glycol, 1,4-cyclohexane dimethanol, and 1,4-butanediol.Aromatic and aliphatic acids which may be used simultaneously to make acopolymer include, for example, isophthalic acid and sebacic acid.

[0023] Preferred catalysts for preparing PTT include titanium andzirconium compounds. Suitable catalytic titanium compounds include, butare not limited to, titanium alkylates and their derivatives, titaniumcomplex salts, titanium complexes with hydroxycarboxylic acids, titaniumdioxide-silicon dioxide-co-precipitates, and hydratedalkaline-containing titanium dioxide. Specific examples includetetra-(2-ethylhexyl)-titanate, tetrastearyl titanate, diisopropoxy-bis(acetyl-acetonato)-titanium,di-n-butoxy-bis(triethanolaminato)-titanium, tributylmonoacetyltitanate,triisopropyl monoacetyltitanate, tetrabenzoic acid titanate, alkalititanium oxalates and malonates, potassium hexafluorotitanate, andtitanium complexes with tartaric acid, citric acid or lactic acid.Preferred catalytic titanium compounds are titanium tetrabutylate andtitanium tetraisopropylate. The corresponding zirconium compounds mayalso be used.

[0024] The polymer of this invention may also contain small amounts ofphosphorous compounds, such as phosphates, and a catalyst such as acobalt compound, that tends to impart a blue hue.

[0025] The melt phase polymerization described above may be followed bya crystallization step, then a solid phase polymerization (SSP) step toachieve the intrinsic viscosity necessary for bottle manufacture. Thecrystallization and polymerization can be performed in a tumbler dryerreaction in a batch-type system. Alternatively, the crystallization andpolymerization can be accomplished in a continuous solid state processwhereby the polymer flows from one vessel to another after itspredetermined treatment in each vessel.

[0026] The crystallization conditions preferably include a temperatureof from about 100° C. to about 150° C. The solid phase polymerizationconditions preferably include a temperature of from about 200° C. toabout 232° C., and more preferably from about 215° C. to about 232° C.The solid phase polymerization may be carried out for a time sufficientto raise the intrinsic viscosity to the desired level, which will dependupon the application. For a typical bottle application, the preferredintrinsic viscosity is from about 0.65 to about 1.0 deciliter/gram, asdetermined by ASTM D-4603-86 at 30° C. in a 60/40 by weight mixture ofphenol and tetrachloroethane. The time required to reach this viscositymay range from about 8 to about 21 hours.

[0027] In one embodiment of the invention, the film-forming polymer ofthe present invention may comprise recycled polyester or materialsderived from recycled polyester, such as polyester monomers, catalysts,and oligomers.

[0028] At least one wall of the container of the present inventioncomprises a populated area. There are technologies that can localize apopulation of particles into one area of a container wall. For example,where the contact surface of the film or wall is the surface adjacent tothe packaged material, the oxygen scavenger could advantageously belocalized in an area at the contact surface. Examples of thesetechnologies include, but are not limited to, lamination, coextrusion,coinjection, and the like. Examples of technologies capable oflocalizing the population are further discussed U.S. Pat. Nos.5,153,038, 6,413,600, 4,525,134, 4,439,493 and 4,436,778 which arehereby incorporated by reference in their entirety. It has now beendiscovered that high levels of particles can be incorporated into filmsor walls made by using these technologies. The localized area in whichthe population of particles is substantially located is referred toherein as the populated area.

[0029] The populated area comprises a population of particles. Thethickness of the populated area is measured cross-sectionally throughthe container wall measuring from the contents side of the package wallto the outer edge of the wall and starts at the first particle of thepopulation and ends when 95% of the population has been accounted for.The thickness of the populated area in a monolayer film or container isthe thickness of film or container wall. In a container wall that is nota monolayer, the thickness of the populated area will be somewhat lessthan the thickness of the wall. The thickness of the populated area of alaminated wall is the thickness of the layer of the wall containing atleast 95 percent of the population of particles. In multilayer films orwalls wherein the layers blend at the interface, such as those formed bycoextrusion, the thickness of the populated area is the cross-sectionalthickness of layer containing at least about 95 percent of thepopulation of particles.

[0030] In the case of two or more distinct populated areas, thethickness of the populated area is reduced by the thickness of theunpopulated area or unpopulated areas lying between the inner andoutermost populated areas. This would be the case of an A−B−A structurewhere A contained the population. The thickness of the populated area isthe thickness of A+B+A−B. in the case of A−B−A−B, the thickness is stillA+B+A−B. Using the same principles, B−A−B−A−B has a thickness ofA+B+A−B. A−B−A−B−A ha a population thickness of 3×A−2×B.

[0031] Preferably, the number of particles in the populated area doesnot exceed a concentration of about (6×10⁷ particles÷T) per cubiccentimeter of polymer, wherein T is the thickness of the populated areain mils. More preferably, the number of particles in the populated areadoes not exceed a concentration of about (3×10⁷ particles÷T) per cubiccentimeter of polymer, wherein T is the thickness of the populated areain mils. Even more preferably, the number of particles in the populatedarea does not exceed a concentration of about (1.5×10⁷ particles÷T) percubic centimeter of polymer, wherein T is the thickness of the populatedarea in mils.

[0032] The population of particles comprises oxygen-scavengingparticles, as well as any other components of the container, such asthose discussed herein, that are present in the form of discreteparticles.

[0033] Suitable oxygen-scavenging particles comprise at least onematerial capable of reacting with molecular oxygen. Desirably, materialsare selected that do not react with oxygen so quickly that handling ofthe materials is impracticable. Therefore, stable oxygen-scavengingmaterials that do not readily explode or burn upon contact withmolecular oxygen are preferred. From a standpoint of food safety,materials of low toxicity are preferred, however with properprecautions, this is not a limitation. The particles should notadversely affect the organoleptic properties of the final product.Preferably, the oxygen-scavenging particles comprise anoxygen-scavenging element selected from calcium, magnesium, scandium,titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper,zinc, silver, tin, aluminum, antimony, germanium, silicon, lead,cadmium, rhodium, and combinations thereof. More preferably, theoxygen-scavenging particles comprise an oxygen-scavenging elementselected from calcium, magnesium, titanium, vanadium, manganese, iron,cobalt, nickel, copper, zinc, or tin. Even more preferably, theoxygen-scavenging particles comprise iron. It will be understood thatthese oxygen-scavenging elements may be present as mixtures, incompounds such as oxides and salts, or otherwise combined with otherelements, with the proviso that the oxygen-scavenging elements arecapable of reacting with molecular oxygen. Metal alloys comprising atleast one oxygen-scavenging element are also suitable. Theoxygen-scavenging particles may contain impurities that do not affectthe practice of the present invention.

[0034] It is known in the art that certain substances enhance the oxygenscavenging reaction. In a preferred embodiment of the present invention,the oxygen-scavenging particles are pre-treated with one or morereaction-enhancing agents that facilitate the oxygen scavengingreaction. Any of the reaction-enhancing agents known in the art may beused.

[0035] In one embodiment of the present invention, the oxygen-scavengingparticles comprise iron. The iron reacts with oxygen in its function asan oxygen scavenger. Metallic iron, or alloys or mixtures containingmetallic iron may be used. Furthermore, it is to be understood that themetallic iron may contain impurities that do not affect the practice ofthe present invention.

[0036] At least three types of metallic iron powders are available:electrolytic, sponge, and carbonyl iron. Electrolytic iron is made viathe electrolysis of iron oxide, and is available in annealed andunannealed form from, for example, OM Group, Inc. Sponge iron isavailable from, for example, North American Höganäs, Inc. There are atleast two types of sponge iron: hydrogen-reduced sponge iron carbonmonoxide-reduced sponge iron. Carbonyl iron powder is available from,for example, Reade Advanced Materials. It is manufactured using acarbonyl decomposition process.

[0037] Depending upon the type of iron selected, the particles may varywidely in purity, surface area, and particle shape. The followingnon-limiting examples of typical characteristics are included herein toexemplify the variation that may be encountered. Electrolytic iron isknown for its high purity and high surface area. The particles aredendritic. Carbonyl iron particles are substantially uniform spheres,and may have a purity of up to about 99.5 percent. Carbonmonoxide-reduced sponge iron typically has a surface area of about 95square meters per kilogram (m²/kg), while hydrogen-reduced sponge irontypically has a surface area of about 200 m²/kg. Sponge iron may containsmall amounts of other elements, for example, carbon, sulfur,phosphorus, silicon, magnesium, aluminum, titanium, vanadium, manganese,calcium, zinc, nickel, cobalt, chromium, and copper.

[0038] The oxygen-scavenging particles are present in an effectiveamount for adequate oxygen-scavenging ability. If too fewoxygen-scavenging particles are present, too much oxygen may be able topass through the container wall without being scavenged. The amountrequired for adequate oxygen-scavenging ability depends on such factorsas the application, the type of polymer used, the amount of gas barrierprotection desired, the type of oxygen-scavenging particles, theparticle size of the oxygen-scavenging particles, and moisture contentof the packaged material. Preferably, the oxygen-scavenging container ofthe present invention comprises at least about 50 partsoxygen-scavenging particles per million parts by weight resin. Morepreferably, the container of the present invention comprises at leastabout 100 parts oxygen-scavenging particles per million parts by weightresin. Even more preferably, the container of the present inventioncomprises at least about 500 parts oxygen-scavenging particles permillion parts by weight resin. Yet even more preferably, the containerof the present invention comprises at least about 1000 partsoxygen-scavenging particles per million parts by weight resin.

[0039] It has been found that containers such as film or bottle articlescomprising up to about 12,000 parts oxygen-scavenging particles permillion parts by weight resin (1.2 weight percent) can have acceptablehaze characteristics. For applications where haze is not an issue ofconcern, it will be appreciated that the amount of oxygen-scavenging orother particles may be much higher. Further characterization of thepopulation of particles that is necessary for practice of the presentinvention is provided hereinbelow.

[0040] The composition of the present invention may optionally furthercomprise one or more reaction-enhancing agents known in the art tofacilitate the oxygen-scavenging reaction. Examples of knownreaction-enhancing agents are discussed in U.S. Pat. Nos. 5,744,056 and5,885,481, hereby incorporated by reference in their entirety. Suitableagents are variously described as hydroscopic materials, electrolyticacidifying agents, non-electrolytic acidifying agents, metal halides,metal sulfates, metal bisulfates, and salts. The reaction-enhancingagents may be added to the polymer melt, or during extrusion.

[0041] The composition of the present invention may optionally yetfurther comprise one or more components selected from the groupconsisting of impact modifiers, surface lubricants, denesting agents,stabilizers, crystallization aids, antioxidants, ultraviolet lightabsorbing agents, catalyst deactivators, colorants, nucleating agents,acetaldehyde reducing agents, reheat reducing agents, fillers, branchingagents, blowing agents, accelerants, and the like.

[0042] It will be understood that if the above-mentioned optionalcomponents maintain their discrete nature within the resin, then theyare part of the population of particles as defined herein.

[0043] High levels of particles can be incorporated into a polyesterresin composition with low haze. The particles may be admixed with thethermoplastic polymer during or after polymerization, with the polymermelt or with the molding powder or pellets from which the injectionmolded articles are formed, or from which the film or sheet is cast.Accordingly, the particles may be added during any of the process steps,such as during melt phase polymerization, after the melt phasepolymerization (post polymerization) but before pelletization, duringsolid state polymerization, and during extrusion. Alternatively, amasterbatch of oxygen-scavenging resin may be prepared, and then mixedor blended with additional resin. Preferably, the masterbatch contains arelatively high amount of particles, and the desired particleconcentration in the product polymer is achieved by mixing or blendingthe masterbatch with an amount of additional resin.

[0044] The container of the present invention advantageously possessesboth effective oxygen-scavenging functionality and acceptable opticalproperties. The optical properties of polymers are related to both thedegree of crystallinity and the actual polymer structure. Transparencyis defined as the state permitting perception of objects through asample. Transmission is the light transmitted. Transparency is measuredas the amount of undeviated light. In other words, transparency is theoriginal intensity of the incident radiation minus all light absorbed,scattered, or lost through any other means.

[0045] Many polymers are transparent, but polymers that are transparentto visible light may become opaque as the result of the presence ofadditives such as fillers, stabilizers, flame retardants, moisture, andgases. The opacity results from light-scattering processes occurringwithin the material. The light scattering reduces the contrast betweenlight, dark, and other colored parts of objects viewed through thematerial and produces a milkiness or haze in the transmitted image. Hazeis a measure of the amount of light deviating from the direction oftransmittancy of the light by at least 2.5 degrees.

[0046] The color and brightness of a polyester article can be observedvisually, and can also be quantitatively determined by a HunterLabColorQuest Spectrometer. This instrument uses the 1976 CIE a*, b*, andL* designations of color and brightness. An a* coordinate defines acolor axis wherein plus values are toward the red end of the colorspectrum and minus values are toward the green end. The b* coordinatedefines a second color axis, wherein plus values are toward the yellowend of the spectrum and minus values are toward the blue end. Higher L*values indicate enhanced brightness of the material.

[0047] Generally, the acceptable haziness of an article, such as abottle or film, is determined visually. However, a HunterLab ColorQuestSpectrometer can quantitatively indicate the haze of an article orresin. This quantitative measurement is referred to herein astransmission Hunter haze.

[0048] It is known in the art that a stretched film will often have morehaze than its unstretched counterpart. Therefore, haze measurements wereobtained on stretched and unstretched container walls and through thebottle itself.

[0049] The container wall of the present invention may compriseunstretched films or sheets. The manufacture of films and sheets isknown in the art, and any one of a number of suitable techniques can beused to prepare the film.

[0050] The container of the present invention may also comprise bottlesexpanded from preforms. A preform is a formed structure that is expandedin a mold to form a bottle. Alternately, the container may comprisefilm, pouches, or other packaging material.

[0051] In general, polyester bottles are prepared in blow-moldingprocesses carried out by heating the preform above the polyester glasstransition temperature, placing the heated preform into a mold of thedesired bottle form, injecting air into the preform to force the preforminto the shape of the mold, and ejecting the molded bottle from the moldonto a conveyor belt.

[0052] Two factors that must be taken into account when accuratelymeasuring haze of stretched material and comparing haze values are thethickness of the article being measured, and the blow window.

[0053] In order to establish the proper temperature and processing timeto obtain the lowest haze value due only to the crystallization processof the polyester resin, a blow window graph is constructed. The blowwindow graph shows haze as a function of the heat exposure time of thepreform. The graph is usually constructed by creating isotherms andheating each preform at the same temperature for different lengths oftime. The heated preform is then stretched and the haze measurement isperformed on the stretched portion. Several different temperatures arechosen. Generally, a resin will have a best temperature that producesthe lowest haze value, and that temperature is used to conduct theremaining evaluations. In the work described herein, one temperature waschosen and the parameter of time was varied to determine the optimumblow window.

[0054] While polyester has excellent optical properties, even whencrystallized through strain hardening (stretching), particulateadditives can reduce the transparency and increase the haze. The numberof particles and the size of the particles affect the haze of bothstretched and unstretched films and articles. It will be appreciated bythose skilled in the art that the thermoplastic resins disclosed hereinvary significantly in density. Additionally, particles of the populationmay vary in density. Therefore, the preferred concentration of thepopulation of particles and scavenging particles within the resin isexpressed as the number of particles per volume of the resin.

[0055] It will be understood that, within any particle population, theparticles are not all the same size, but comprise a range of particlesizes. Furthermore, the particles within the population may or may nothave a uniform, regular shape. The particle population, or any portionof the population, may be described by an average particle size, asmeasured by any of the standard techniques known in the art. Thesetechniques include measuring the equilibrium velocities of particlessettling through a liquid under the influence of gravity, resistancepulse counters, light blockage counters, image analyzers, laserdiffraction spectroscopy, and photon correlation spectroscopy.Statistical values commonly used to describe the particle size of aparticle population include: (1) geometric mean size, which is theaverage particle size calculated on a log basis; (2) arithmetic mean,which is the average particle size calculated on a linear basis; (3)median size, which is the 50^(th) percentile of the distribution; and(4) mode size, which is the most prevalent particle size of thedistribution. Further, the sample may be described by a particle sizerange, or as less than or equal to a given particle size. Thesedesignations may be determined by sieving techniques, or othertechniques known in the art. Thus, any given population of particleswill have a particle size distribution, which is a description of therange of particle sizes and the amounts of particles of each size.Techniques for particle size determination are further discussed by PaulWebb and Clyde Orr in Analytical Methods in Fine Particle Technology,Micromeritics Instrument Corp. (1997), and by James P. M. Syvitski inPrinciples, Methods, and Applications of Particle Size Analysis,Cambridge University Press (1991), both of which are hereby incorporatedby reference in their entireties.

[0056] Various parameters have been found to be desirable for the sizeof particles within the particle population. For example, it will beappreciated that particles larger than the thickness of the containerwall may produce a rough surface, so that significant amounts of suchlarge particles are to be avoided. In general, it is preferred that thesize of the particles fall within the range of from about 1 to about 70microns, more preferably from about 10 to about 70 microns, and evenmore preferably from about 15 to about 70 microns. Even yet morepreferably, that the size of the particles fall within the range of fromabout 20 to about 70 microns. It will be understood that these preferredranges are given as general guidelines only, and that a small number ofparticles may fall outside these ranges without affecting the essentialcharacteristics of the resin, and are therefore within the scope of thepresent invention.

[0057] Recitations throughout the specification and claims of “do notexceed about 6.0×10⁷” are intended to include smaller amounts ofparticles, depending upon the amount that is preferred. Desirably, largeamounts of particles are added to the resin and the impact on haze isminimized. This can be accomplished by selecting the particle sizedistribution of the population of particles, and controlling the totalnumber of particles to keep it below a certain maximum value per unitvolume of polymer. This maximum value is related to thickness of thepopulated resin.

[0058] High levels of particles can be incorporated into a containerwall with low haze by a method comprising the steps of: providing apopulation of particles; selecting the particle size distribution of thepopulation to comprise an appropriate number of particles within thepreferred size range; adding the population of particles to a polymer toform a mixture of polymer and particles during one or more of theprocess steps of: melt phase polymerization of the polymer; postpolymerization and prior to pelletization; solid state polymerization ofthe polymer; and extrusion; and forming a container having at least onewall by using the mixture of polymer and particles.

[0059] As discussed above, the population of particles may be localizedinto one or more populated areas of a container wall, by varioustechnologies. In this embodiment, the populated area comprises themixture of polymer and particles, and the method further comprises thestep of combining the mixture with additional polymer to form a wallhaving a populated area and at least one other area. The additionalpolymer may be a different polymer or the same polymer but without anyscavenger present.

[0060] The container, according to the present invention, can compriseunstretched films or sheet of any thickness typically employed in theart of polymer films.

[0061] In a preferred embodiment, the film has a thickness of at leastabout 0.5 mils, and a transmission Hunter haze number of, preferably,less than about 10 percent, more preferably less than about 8 percent,and even more preferably less than about 5 percent. While higher thanthe haze numbers for polyester samples comprising no oxygen-scavengingor other particles, these haze values are well within the range ofvalues acceptable for many commercial applications.

[0062] The container can comprise bottles wherein each bottle sidewallhas a thickness of from about 9 to about 35 mils, preferably from about11 to about 25 mils, and more preferably from about 14 to about 21 mils.

[0063] In a preferred embodiment, each bottle sidewall has a thicknessof from about 14 to about 21 mils, and the bottle has a Hunter hazenumber of, preferably, less than about 10 percent, more preferably lessthan about 8 percent, and even more preferably less than about 5percent, at optimum blow window conditions. While higher than the hazenumbers for polyester samples comprising no iron or other particles ofoxygen-scavenging composition, these haze values are well within therange of values acceptable for many commercial applications.

[0064] The maximum preferred concentrations of particles recited abovewere determined for unstretched films having a crystallinity of lessthan about one percent. In general, as the crystallinity of the polymerresin increases, haze increases. It will therefore be understood thatthe maximum preferred concentration of particles will be lower inpolymer compositions having higher crystallinity

[0065] In order to demonstrate the practice of the present invention,the following examples have been prepared and tested as described in theGeneral Experimentation Section disclosed herein below. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

GENERAL EXPERIMENTATION Preparation of Examples Nos. 1-26

[0066] A PET copolymer resin was prepared by the teachings of U.S. Pat.No. 5,612,423 that is incorporated herein by reference. Samples of ironparticles having various particle sizes were obtained. Hydrogen-reducedspong iron from Pyron was used for examples 1-10. Carbonyl iron powderobtained from ISP Technologies was used for examples 11-26. Thus, theiron particles used in Example No. 3 had a particle size range of about25 to about 38 microns. It will be understood that such a sample can beprepared, for example, by using sieves. The iron particles were added topolyester resin, by using a metered feeder on a twin-screw extruder, toform a masterbatch of resin containing 2.5 percent by weightiron-containing resin composition. This masterbatch was blended with thebase resin to obtain the desired concentration. The base resin/ironmixtures were dried under vacuum at 325° F. (163° C.) for 18 hours. Thedried resins were transferred to is a Novotec drying hopper of a NisseiASB 50T Injection Blow-Molding machine. The hopper was heated to 325° F.(163° C.) and set for a dew point of −40° F. (−40° C.).

[0067] The bottle preforms were manufactured and blown into bottles in atwo-step process. First, the preforms were prepared on a Mini-jector orNissei machine. Then, the bottles were blown from their preforms on aCincinnati Milacron Reheat Blow Lab (RHB-L) blow molding machine. Thepreforms were prepared on the Mini-jector using a cycle time of 45second, inject time of 15 seconds, with a rear heater temperature of270° C., a front heater temperature of 275° C., and a nozzle heat of275° C. The inject pressure was between about 1000 and about 1500 psig.The oven temperature on the Milacron RHB-L was from about 163 to about177° C. The exposure time was from about 31 to about 52 seconds.

[0068] The haze measurements were taken through the bottle sidewall,which is the thinned, stretched portion. Because these measurements weretaken on the whole bottle, the thickness actually contains twosidewalls. A HunterLab ColorQUEST Sphere Spectrophotometer Systemequipped with an IBM PS/2 Model 50Z computer, IBM Proprinter II dotmatrix printer, assorted specimen holders, and green, gray and whitecalibration tiles, and light trap was used. The HunterLabSpectrocolorimeter integrating sphere sensor is a color and appearancemeasurement instrument. Light from the lamp is diffused by theintegrating sphere and passed either through (transmitted) or reflected(reflectance) off an object to a lens. The lens collects the light anddirects it to a diffraction grating that disperses it into its componentwave lengths. The dispersed light is reflected onto a silicon diodearray. Signals from the diodes pass through an amplifier to a converterand are manipulated to produce the data. Haze data is provided by thesoftware. It is the calculated ratio of the diffuse light transmittanceto the total light transmittance multiplied by 100 to yield a “Haze %”(0% being a transparent material, and 100% being an opaque material).Samples prepared for either transmittance or reflectance must be cleanand free of any surface scratches or abrasions. The size of the samplemust be consistent with the geometry of the sphere opening and in thecase of transmittance, the sample size is limited by the compartmentdimension. Each sample is tested in four different places, for exampleon the bottle sidewall or representative film area.

[0069] A Panametrics Magna-Mike 8000 Hall Effect Thickness Gauge wasemployed to measure the bottle sidewall thickness. A small steel ball isplaced on one side of the test material and a magnetic probe underneath.The distance between the ball and the probe is measured by means of theHall effect sensor. More specifically, a Magna-Mike 8000 equipped with aDPU-411 thermal printer (type II), a remote foot switch, a target ballkit, and a Standard 801PR Probe was used. Two measurements were takenand averaged.

[0070] The iron particle concentration, average iron particle size, andthe haze values at a constant sample thickness of from about 11 to about13 mils and optimum blow window conditions are summarized in Tables 1and 2. Comparative Example Nos. 1, 6, and 11 contained no ironparticles. The particle size of the iron particles reported in Table 1was provided by the supplier. The particle size of the iron particles inTable 2 were determined as the geometric mean based upon volume. TABLE 1Iron Particles in Stretched Polyester Film Compositions Optimum Fe conc.Particle size reheat time Example No. (ppm) (microns) (sec) Haze (%) 1  0 — 43 1.5 2 1250 ≦25 49 7.56 3 1250 25-38 49 4.53 4 1250 38-45 524.58 5 1250 45-75 52 4.41 6   0 — 43 1.5 7 2500 ≦25 46 14.08 8 250025-38 46 9.13 9 2500 38-45 46 8.45 10 2500 45-75 40 8.56

[0071] TABLE 2 Iron Particles in Stretched Polyester Film Compositionsand Haze Values No. of particles Particle per cm³ Optimum Example Feconc. size polymer reheat Haze No. (ppm) (microns) (×10⁶) time (sec) (%)L* 11  0 — 0 43 1.5 90.89 12 100 3.23 0.3729 46 5.1 89.78 13 250 3.230.9324 40 6.98 88.66 14 500 3.23 1.8647 46 9.12 86.17 15 800 3.23 2.983646 11.63 83.99 16 1000  3.23 3.7295 46 16.44 78.1 17 100 4.787 0.0750 494.55 89.76 18 250 4.787 0.1875 49 6.74 89.73 19 500 4.787 0.3750 46 9.0488.27 20 800 4.787 0.5999 46 11.8 87.21 21 1000  4.787 0.7499 46 12.9983.68 22 100 7.819 0.0483 49 5.4 90.51 23 250 7.819 0.1207 46 6.85 89.8324 500 7.819 0.2415 43 8.49 88.79 25 800 7.819 0.3864 49 7.83 88.06 261000  7.819 0.4830 46 8.81 87.27

Preparation of Examples Nos. 27-32

[0072] Examples 27 through 32 are also stretched film samples preparedas above. Results are shown in Table 3. The type of iron used forExamples 27-29 was unannealed electrolytic iron having a geometric meanparticle size based upon volume of about 10.84 microns. The iron usedfor Examples 30-32 was carbon monoxide-reduced sponge iron having ageometric mean particle size based upon volume of about 18.61 microns.While the parts iron by weight per million parts by weight polymer arecomparable, the number of particles per cubic centimeter polymerincrease with decreasing particle size, and the transmission Hunter hazeper mil thickness of the film also increases. It should be noted thatfor examples 27-32, the haze measurement was taken on the bottlesidewall only and was not taken through the complete bottle. TABLE 3Variation of Particle Size, Number of Particles, and Haze No. ofParticles PPM Iron per cc³ Polymer Thickness Haze per mil Example No.(by weight) (×10⁶) (mils) (%) 27 1000 0.2183 13.0 0.257 28 2000 0.436511.0 0.532 29 3000 0.6548 13.0 0.630 30 1000 0.0296 11.0 0.094 31 20000.0593 11.0 0.155 32 3000 0.0889 11.0 0.254

Preparation of Examples Nos. 33-44

[0073] In order to investigate the optimum concentration of particles ofvarious sizes in unstretched resin, films were made by using a Haakemixer. 2500.0 grams of HiPERTUF 89010 copolyester resin was weighed intoeach of several 1-gallon cans and dried in a vacuum oven under fullvacuum at about 100° C. overnight. The vacuum was restored toatmospheric pressure with nitrogen. Appropriate amounts of carbonyl-typeiron powder, manufactured by ISP Technologies was weighed under nitrogeninto vials for the different concentrations desired. The nominalparticle size range of the iron provided by the supplier was about 7 toabout 9 microns. The geometric mean particle size based on volume forthis iron powder was about 7.819 microns. The iron was added to theresin just prior to removing the hot resin from the oven, the vials weresealed, and the mixture was blended on a roller mill for about 5minutes.

[0074] The blended mixture was added to the feed hopper of a HaakePolylab extrusion system for film production. The resin was melted inthe extruder and forced out of the die in the form of a flat sheet. Thethin, unoriented, substantially amorphous film was fed through a 3-rolltemperature-controlled polishing stack, quenched to minimizecrystallinity and to give a final, polished surface. The cooled film waswound onto a core. The thickness of the films measured in mils, thepercent transmission Hunter haze, and the percent haze per mil fortypical film samples having a constant concentration of iron are shownin Table 4. The concentration of iron is about 0.9659×10⁶ particles percubic centimeter polymer for Examples 33 and 34, and about 2.8978×10⁶particles per cubic centimeter polymer for Examples 35-37. It can beseen that, while haze increases with increasing film thickness, the hazeper mil of film thickness stays constant.

[0075] In Examples 38-44, the thickness of the films was kept constantat about 11 mils, number of particles per cubic centimeter of polymerwas varied. It can be seen that the haze per mil thickness increaseswith increasing particle concentration. TABLE 4 Dependency of Haze onThickness of Populated Area (T) Thickness T Example No. Fe Conc (ppm)(mils) Haze (%) Haze/mil 33 2000 11 2.17 0.197 34 2000 15 3.07 0.2056000 35 6000 11 5.29 0.481 36 6000 15.3 6.68 0.437 37 6000 20 8.78 0.439

[0076] TABLE 5 Dependency of Haze on Number of Particles No. ofParticles Fe per cm³ Polymer Thickness T Example No. Conc (ppm) (×10⁶)(mils) Haze/mil 38   0 0 10 0.035 39 1000 0.483 11 0.127 40 2000 0.965911 0.197 41 3000 1.4489 11 0.302 42 6000 2.8978 11 0.481 43 10000 4.8297 11 0.745 44 12000  5.7956 10.7 0.880

[0077] Haze values of less than 10% are obtained, even at iron levels of2500 ppm, when the iron particle size is greater than about 25 microns,as shown in Table 1. At 1250 ppm iron, and also at 2500 ppm iron, thehighest haze values were obtained when the average particle size wasless than or equal to about 25 microns, i.e., Example Nos. 2 and 7,respectively. Nevertheless, when the iron particle size is less than orequal to about 25 microns, haze values of less than 10% are obtained atiron levels up to about 1250 ppm. As shown in Table 2, when the ironparticle size is less than or equal to about 8 microns, haze values ofless than 10% are obtained at iron levels up to about 800 ppm.Furthermore, when the iron particle size is less than or equal to about5 microns, haze values of less than 10% are obtained at iron levels upto about 500 ppm.

[0078] When the population of particles is a constant parts by weightper million parts polymer, the number of particles per cubic centimeterof polymer decreases as the particle size increases, as shown in Table3. The overall transmission Hunter haze increases as the thickness ofthe sample increases, as shown in Table 4, however the haze per mil ofthickness stays relatively constant. Haze values of less than 1.0% permi of a container wall are obtained at concentrations of particles of upto (6×10⁷ particles÷T) per cubic centimeter of polymer, wherein T is thethickness of the populated area in mils, as shown in Table 5.

[0079] As should now be understood, the present invention overcomes theproblems associated with the prior art by providing a thermoplasticresin composition which contains an effective amount ofoxygen-scavenging particles and which has acceptable color and hazecharacteristics. The resulting resin can be used to form transparentbottles, films, and other containers and packaging materials. Thesematerials comprise oxygen-scavenging particles in an amount sufficientto effectively scavenge oxygen and provide longer shelf life foroxygen-sensitive materials. Furthermore, these materials have acceptablehaze characteristics.

[0080] While the best mode and preferred embodiment of the inventionhave been set forth in accordance with the Patent Statutes, the scope ofthis invention is not limited thereto, but rather is defined by theattached claims. Thus, the scope of the invention includes allmodifications and variations that may fall within the scope of theclaims.

What is claimed is:
 1. A container having at least one wall, wherein thewall comprises a populated area, and wherein the populated areacomprises: a film-forming polymer; and a population of particlescomprising an effective amount of oxygen-scavenging particles, whereinthe number of particles of said population does not exceed aconcentration of about (6×10⁷ particles÷T) per cubic centimeter ofpolymer wherein T is the thickness of the populated area in mils; andwherein said wall has a transmission Hunter haze of up to about 1percent per mil of the container wall.
 2. The container of claim 1,wherein said polymer comprises polyester.
 3. The container of claim 2,wherein said polyester comprises linear polyester.
 4. The container ofclaim 3, wherein said polyester comprises polyethylene terephthalate,copolymers of polyethylene terephthalate, polyethylene naphthalate,copolymers of polyethylene naphthalate, polybutylene terephthalate,copolymers of polybutylene terephthalate, polytrimethyleneterephthalate, or copolymers of polytrimethylene terephthalate.
 5. Thecontainer of claim 2, wherein the polyester is prepared from one or morepolyfunctional comonomers.
 6. The container of claim 5, wherein saidpolyfunctional comonomers are selected from the group consisting ofpyromellitic dianhydride and pentaerythritol.
 7. The container of claim1, wherein said effective amount is at least about 50 parts per millionby weight oxygen-scavenging particles per million parts by weightpolymer.
 8. The container of claim 1, wherein said oxygen-scavengingparticles comprise at least one of calcium, magnesium, scandium,titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper,silver, zinc, tin, aluminum, antimony, germanium, silicon, lead,cadmium, rhodium, or combinations thereof.
 9. The container of claim 2,wherein said oxygen-scavenging particles comprise at least one ofcalcium, magnesium, scandium, titanium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, silver, zinc, tin, aluminum, antimony,germanium, silicon, lead, cadmium, rhodium, or combinations thereof. 10.The container of claim 3, wherein said oxygen-scavenging particlescomprise at least one of calcium, magnesium, scandium, titanium,vanadium, chromium, manganese, iron, cobalt, nickel, copper, silver,zinc, tin, aluminum, antimony, germanium, silicon, lead, cadmium,rhodium, or combinations thereof.
 11. The container of claim 4, whereinsaid oxygen-scavenging particles comprise at least one of calcium,magnesium, scandium, titanium, vanadium, chromium, manganese, iron,cobalt, nickel, copper, silver, zinc, tin, aluminum, antimony,germanium, silicon, lead, cadmium, rhodium, or combinations thereof. 12.The container of claim 1, wherein said oxygen-scavenging particlescomprise iron.
 13. The container of claim 2, wherein saidoxygen-scavenging particles comprise iron.
 14. The container of claim 3,wherein said oxygen-scavenging particles comprise iron.
 15. Thecontainer of claim 4, wherein said oxygen-scavenging particles compriseiron.
 16. The container of claim 1, wherein said oxygen-scavengingparticles comprise iron, and wherein said oxygen-scavenging particlesare present in an amount of from about 50 to about 12,000 parts permillion by weight of the resin.
 17. The container of claim 1, whereinsaid polymer further comprises one or more components selected from thegroup consisting of impact modifiers, surface lubricants, denestingagents, stabilizers, crystallization aids, antioxidants, ultravioletlight absorbing agents, catalyst deactivators, colorants, nucleatingagents, acetaldehyde reducing agents, reheat reducing agents, fillers,branching agents, blowing agents, and accelerants.
 18. The container ofclaim 1, wherein said population of particles further comprisesreaction-enhancing particles.
 19. The container of claim 18, whereinsaid reaction-enhancing particles comprise hydroscopic materials,electrolytic acidifying agents, non-electrolytic acidifying agents,metal halides, metal sulfates, metal bisulfates, or mixtures thereof.20. The container of claim 1, wherein said oxygen-scavenging particlesare pretreated with at least one reaction-enhancing agent.
 21. Thecontainer of claim 1, wherein said container is a stretched bottlehaving a sidewall thickness of from about 11 to about 25 mils and aHunter haze value of about 10% or less.
 22. The container of claim 2,wherein said container is a stretched bottle having a sidewall thicknessof from about 11 to about 25 mils and a Hunter haze value of about 10%or less.
 23. The container of claim 3, wherein said container is astretched bottle having a sidewall thickness of from about 11 to about25 mils and a Hunter haze value of about 10% or less.
 24. The containerof claim 4, wherein said container is a stretched bottle having asidewall thickness of from about 11 to about 25 mils and a Hunter hazevalue of about 10% or less.
 25. The container of claim 1, wherein saidpopulated area comprises a laminated layer of the wall of the container.26. The container of claim 1, wherein said populated area comprises acoextruded layer of the wall of the container.
 27. The container ofclaim 1, wherein said thickness of said populated area is equal to thethickness of the container wall.
 28. The container of claim 1, whereinthe thickness of said populated area is less than the thickness of saidcontainer wall.
 29. The container of claim 1, wherein said container isa tray.